Gaseous electric discharge device



Feb. 11, 1936. c. E. KENTY GASEOUS ELECTRIC DISCHARGE DEVICE Filed April 25, 1932 INVENTOR I B 6x197? awe I L A RNEY Patented Feb. 11, 1936 PATENT OFFICE GASEOUS ELECTRIC DISCHARGE DEVICE Carl a. 1mm. Jersey City, N. 1.. assignor to General Electric Vapor Lamp Company, Hoboke'n, N. J a corporation of New Jersey Application April 25, 1932, Serial No. 607,445

13 Claims. (Cl. 176-124) The present invention relates to gaseous electric discharge devices generally, and more particularly todischarge devices operating with a long positive column discharge.

A particular object of the invention is to provide a gaseous .electric discharge device of the positive column type in which a discharge may be initiated by the application of a potential of less than 110 volts D. C. between the electrodes thereof. A further object of my invention is to provide a novel method of starting and operating an electric gaseous discharge device. Still other objects and advantages of my invention will appear from the following detailed description thereof, or from an inspection of the accompanying drawing.

The invention consists in a new and novel electric gaseous. discharge device, and in a novel method of operation thereof, as hereinafter set forth and claimed. I

Electric gaseous discharge devices in their nor mal unionized state offer a very considerable resistance to the passage of an electric discharge therethrough, with the result that it is usually necessary to apply a voltage very much in excess' of the normal operating potential in order to initiate a discharge therethrough. This has tended to restrict the use thereof, since any of these devices having positive columns of appreciable length could not be operated directly from the usual distribution circuits of 110 volts A. C.

or D. C., auxiliary apparatus invariably being necessary to start the discharge. I have now discovered that a resistance wire placed along the arc path and connected to the anode may be effectively used to reduce the ratio between the breakdown potential and the arc maintainlng potential of the device, this wire being especiaily effective if its resistance per unit length. of the arc path progressively increases towardthe cathode. It is likewise desirable that the surface area per unit length should decrease toward the cathode. During starting, when a dis-' charge initially takes place through the relatively short gap between the cathode and the free end of this wire, this distribution of the resistance continuously produces the highest possible potential gradient in' that portion of the wire which the discharge is approaching, so that this discharge is transferred up. the arc tube to the anode with cclerity. As a result it has been found possible tostart tubes of very considerable length, and containing any desired gaseous atmosphere, by application of a potential but little in excess of the are maintaining Potential.

The aforesaid distribution of the resistance has also been found to produce a substantially uniform potential gradient throughout the length of the wire during maintenance of the discharge. As a result all parts of the wire are at a uniform potential with respect to the adjacent discharge, so that sputtering of the wire due to ionic bombardment thereof, with itsattendant blackening of the envelope and clean-up of the gas, is avoided. While this wire is very eflective in starting discharge of appreciable length on potentials of the order of 100 volts D. C., I have found that even longer discharges may be started at the same potential by use of a gas mixture such as proposed in Patent 1,990,175, granted to Ted E. Foulke Feb. 5,-1935. In this casethe discharge creeping along the resistance wire serves to emit radiations which ionize the gas an appreciable distance in advance of the discharge, this in turn promoting the advance of the dis- 2o charge along the wire. .With such a combination it has been found possible to start, a discharge by application of a potential but 15% in excess of the normal are maintaining voltage, with the result that but little wattage needs to be absorbed by the ballast resistance. A phenomenally high efllciency is therefore obtainable with this novel device.

For the purpose of illustrating my'invention I have shown several embodiments thereof in the accompanyin'g'drawing, in which Fig. 1 is an elevational view, in part section, of a lamp especially designed for use on direct current, V

Fig. 2 is an elevational view, in part section, of a modification of the device ofFlg. 1 for use on alternating current, and

Fig. 3 is an elevational view of another modification of the device of Fig. 1 which is also intended for use on alternating current. 40

In the drawing, with special reference to Fig.

1, the tubular envelope I of glass or other vitre I ousmaterlal has at one end a thermionic cath-' ode 2 which preferably consists of a cellular electrode which closely surrounds a heater 3. Said cathode 2 is itself surrounded by the tubular heat conserving shields 4 and 5 to which it is electrically connected, the heat shield 5 preferably extending some distance beyond said cathode I.

Said heater 3 isdesigned for operation on 110 volts, .hence the heating coil thereof (not shown) is completely embedded in a suitable refractory material, such as alundum, in order to prevent the'formation of an are between diflerent portions thereof. One end of said heating coil is connected to an inlead 0, which is also suitably shielded to prevent the formation of an arc thereto, while the other end of said heating coil is electrically connected to the cathode 2. The inlead I is attached to the heat shield 5, and

hence is likewise electrically connected to the cathode 2. Said cathode 2 and the heat shields l and 5 are conveniently formed of nickel or the like. The inner surfaces of said cathode 2 are preferably coated with an alkaline earth metal or compound thereof, in order to reduce the work function of these surfaces. For instance. I prefer to use a mixture of barium and strontium oxides, these oxides being conveniently reduced from the carbonates in situ by the use of heat in a well known manner. In some cases I also coat that portion of the inner surfaces of the heat shields! and '5 which extends beyond the cathode 2 with a material, such as powdered'aluminum, which is known to resist activation by particles sputtered from the active cathode surface, in order to permanently confine the discharge to the desired surfaces within the cathode 2. At the opposite end of the envelope I there is an anode 0 of graphite, iron, or other suitable material, said anode being supported by an inlead 9. An inlead l0 extends to a point just beyond said anode and supports one end of a resistance wire II. ,The other end of said resistance wire terminates in a very small collector I! of tungsten, nickel, iron, or the like which issuitably supported near the cathode 2, although in some cases this collector may be omitted, the end of the wire then performing the function thereof.

Said resistance wire may consist of a refractory v metal such as tungsten, but the nickel-chromium alloy known to the trade as Nichrome" is preferred due to the greater specific resistance thereof. It has been found that to obtain the maximum advantage from this wire the resistance thereof per unit length along the arc path should a progressively increase in the direction of the spaced progressively cathode, while the surface area thereof per unit length along the arc path should progressively increase in the direction of the anode. These conditions may be met by using a tapered conductor, the smaller end of which is attached to the collector l2. Such a tapered conductor is necessarily extremely fragile, however, since in the interest of lamp eillciency a wire approximately 20 inches long must have an appreciable resistance, of the order of 50-300 ohms, hence I prefer to use alarger wire wound in the form of a spiral whose turns decrease in diameter in the direction of the cathode, the pitch of these turns likewise progressively decreasing in the same direction, said pitch decreasing faster than said diameter .in order to concentrate the 1 :sistance at the cathode end. In practice I have found a n1- chrome wire of about 6 mils diameter, wound on a mandrel having a diameter of 35 mils at the small end and 125 mils at the larger end, with the turns practically contiguous at the small end 1 and that at the larger endof a-spiral twenty inches long the resistance per unit length along the axis of the spiral is of the order of a tenth that at the small end, to give good results. In some cases I form successive lengths of the spiral in the-direction of the anode of increasingly larger wire,

each section of a particular size wire having the' turns so spaced that the desired variation in resistance per unit length along the axis is produced. With the latter'construction the turns at the larger end of the spiral may still be quite of another gas having said sleeve being positive,

farther apart at such a rate ized discharges, or hot spots",

' the resistance wire close together with the result that the space charge about the adiacent turns of the spiral causes the spiral to function like the contiguous tapered conductor mentioned above. Any desired gaseous atmosphere may be employed within the envelope I, such as argon, neon, helium, mercury vapor or the like. For example, pure neon has been successfully of 0.5-3.5 mm. of mercury. With such an atmosphere a device having a positive column an inch in diameter and 15-18 inches long may be successfully startedand operated on volts D. C. Where longer positive columns are I find it advantageous to add a small percentage an ionizing potential of the same order as a metastable potential of the main gas, ,asdisclosed in the Foulke patent hereinbefore referred to. For example, where neon is employed as the main gas I find that the addition of 0.2% of argon materially increases the length used at pressures of the order of positive column which may be started on a given voltage.

A screw base l3 of a conventional type is al.- flxed to the cathode end of the envelope I, the heater inlead 6 being connected to the tip thereof, while the cathode inlead l is connected to the sleeve. A conducting cap I4 is afllxed to the anode end of said envelope, the anode lead I being connected thereto through a ballast resistance is, of the order of 10-25 ohms, while the inlead II is likewise connected to said cap throughsaid resistance i5 ahd an additional resistance Ii, of the order of 6 ohms. Said resistance I0 is shown external to the envelope i, but may be sealed therein, if desired, between'the anode 0 and the adjacent end of the envelope.

num foil or the like which extends along the sur- Thus the device may be face of the envelope l startedand operated by simply screwing the base I! into a socket of any 110 volt direct current line, without any auxiliary may also be operated with a half-wave discharge directly on a 110 volt alternating current line, if desired. In order to facilitate the dissipation of heat from the resistances l5 and It the cap I4 is preferably perforated to allow passage of air currents thenethrough.

In the use and operation of this device, upon the application of a suitable direct current potential between the tip and sleeve of the base it, potential will be applied between the anode 8 and the cathode 2, but this potential is insufllcient to produce the desired arc discharge through the gas in its unionized state. Potential is likewise impressed between the collector I2 and the cathode l, but the separation therebetween is purposely made large enough that no appreciable current can flow therebetween until the cathode 2 has reached such a temperature that its free electron emission can support the normal discharge current, in

order to avoid the formation of destructive localon said cathode, such as invariably accompany premature initiation of the main discharge. Current flows,'however, through the heater 3, gradually raising the cathode, temperature until the desired emission is obtained. A discharge thereupon starts between thecollector i2 and the cathode 2. This dischargeadvances virtually instantaneously up ii toward the anode 0 for two reasons. Due to the progressively decreasing resistance of the wire ii per unit length of the disapparatus. The device chargepath toward said anode there is continuoualy a steep potential gradient in said wire immediately in advance of the discharge which eausesthe discharge. to spread rapidly toward the anode, while at the same time the constantly increasing eflective surface area of the wire II per unit length of the discharge path in the direction of the anode 8 causes a constantly de-' creasing anode fall as the discharge extends toward said anode, this factor also contributing to the desired rapid extension of the discharge up w reached the anode end of the resistance wire II it immediately extends to the anode 8, due to the fact that the surface of said anode is so much larger than that of the wire I I that the anode fall is much lower thereto, and to the fact that it is at somewhat higher potential than said wire, as a result of the voltage drop in the resistance I6. The main discharge between the anode II and the cathode 2 is thus initiated and continues independently of the wire II. Said wire continues to pick up energy from the discharge throughout its length, however. The resulting current flow therein varies substantially inversely as the reaistance per unit length of the wire and thus produces a substantially uniform potential gradient. in the wire. Since the space potential along the discharge path likewise has a uniform gradient exoept in the immediate vicinity of the main elec-' trodes it is apparent that all parts of the wire II will operate at substantially the same relative potential with respect to space. This relative potential is moreover very small, due to the fact that the anode end of the wire I I is connected to the anode 8 through the low resistance IS, in which the voltage drop is small. As a result there is no sputtering bombardment of this wire by positive ions from the discharge, so that the presence of the wire II does not in any way shorten the life of the device, as it would if parts thereof were appreciably negative with respect to space, in which case particles would be rapidly sputtered therefrom. The resistance IS, in addition to facilitating the transfer of the discharge to the anode Operation of the device, for it limits the current which may be collected by the wire II to a safe value, thus preventing overheating of this wire. While the various phases of the starting operation have been described as, being sequential it is to be understood that once the discharge starts from the collector I2 the main discharge from the anode 8 follows so soon thereafter that there ,is no discernible time lag. As a result devices of the type illustrated in Fig. 1 maybe successfully operated with a half-wave discharge on 60 cycle alternating current, where the arc must be reinitiated on every alternate half cycle.

. Where a gas mixture is used, as hereinbefore proposed, the discharge creeping up the wire II sends out resonance radiations in advance thereof which produce excited atoms of the principal gas. Many of these excited atoms gain or lose enough energy through collisions toenter a metastable'state. These metastable atoms in turn collide with and thus ionize atoms of the gas of lower ionizing potential. The presence of this ionization in advance of the discharge greatly facilitates the extension of the discharge along the wire, and makes possible the starting of much nected to a suitable alternating current line.

3, plays an important role during the longer'positive column discharges, with a given voltage. This in turn permits the production of a more efllcient device, for the ratio of operating to line voltage is higher where the column is longer, as is obvious, so that a smaller portion, of the energy is absorbed in the ballast resistance I5. I have found, for example, that by using the neon-argon mixture hereinbefore described in my novel discharge device I can initiate a discharge on 110 volts which requires an are maintaining potential'of from 90 to 95 volts, so that only a very small percentage of the energy needs to be absorbed by the ballast. The overall efliciency of these devices is, therefore. unusually high.

Fig. 2 shows how my invention may be employed in an alternating current lamp of the selfrectifying type. 2| of any suitable vitreous material and has a conventional oxide coated cathode 22 at one end thereof, within which there is a low voltage filamentary heater 23. A. heat shield 24 is placed about said cathode 22 if desired. One end'of said heater 23 is connected to said cathode 22, while the other end thereof is connected to the inlead 26. Said cathode 22 is supported by the inlead 21. Two anodes. 28 are provided at the opposite end of said envelope 2 I, each of said anodes being supported by aninlead 29. An inlead III 'is sealed into said envelope 2| between the anodes 23 and supports a resistance wire II which is a counterpart of the resistance employed in the device of Fig. 1, the lower end of said wire being attached to' the very small current collector I2 which is suitably fixed within said envelope 2I at apoint near the cathode 22. The envelope 2I has sealed therein any desired gaseous atmosphere, such as neon, helium, argon, mercury or the like at a low pressure, such as has been described in tion with the device of Fig. l.

The cathode inlead 21 of this device is connected through an arc stabilizing inductance 30 to v themid-point of an autotransformer 3 I, while the ends of said autotransfonner are connected to the anode inleads 29 through the ballast resistances 32. Said autotransformer is in turn con- A low voltage secondary 33 has its ends connected to the leads 26 and 21, and thus serves to energize the heater 23. A rectifier 34 is connected to each anode lead 29, the negative side of each of said rectifiers being connected to a common point,

This lamp has a sealed envelope connecfrom which a connection is made through the resistance I6 to the inlead Ill. Where the rectiflers 32 have appreciable effective resistance theresistance I6 is reduced or omitted.

The starting and operation of this device is in many respects similarto that of the device of Fig. 1. Due to the connection of the wire II to each of the anodes 28 through the rectifiers 34 it is in effect directly connected to each anode while it is positive with respect to the cathode 22 and disconnected therefrom when it is negative with respect thereto. Thus assuming that the discharge first takes place from the collector I2 to the cathode 22 on a given half cycle, the discharge will spread along the wire I I to the proper anode in exactly the same manner as described in connection with the device of Fig. 1. At the end of that half cycle the main discharge automatically transfers to the otheranode 23 in a well known manner, and the connection of the wire II is also, in effect, transferred'to the same anode. Thus as a result of the novel connection of this wire through the two rectifiers all parts the use of additional thereof are always maintained at substantially the samepotential as space, so that there is no appreciable sputtering thereof by ionic bombardment. The wire II is, therefore, as effective and desirable in this, alternating current lamp as it is in the direct current lamp of Fig. l. i

In some cases one of the rectifiers 34 and its leads may be omitted, leaving the inlead l0 connected to only one of the" anode inleads 29. With this circuit the wire II is in effect directly connected to an anode, as in the direct current case, during one half cycle, and left floating during the other half cycle. The starting of the main discharge is not appreciably affected by this, being delayed at most only an extra half cycle. But during the floating half cycle parts of the wire II will obviously be at a considerable negative potential with respect to space, so that these parts of the wire will be subjected to,ionicbombardment and sputtering during this half cycle. With higher gas pressures this is relatively unimportant, however, due to the lower velocity of the positive ions.

In case the anodes themselves are connected to the autotransformer through rectifiers, as in some of the rectifier circuits which are now well known, rectifiers 34 is, of course, unnecessary, since the function thereof will be fully' performed by the rectifiers in the anode leads. I The device of Fig. 3 has a sealed envelope I, each end of which is identical with the cathode end of the device of Fig. 1, and due to thissymmetry is especially adapted for full-wave operation on alternating current. Two inleads l3 are thus provided, each of which supports a wire -il which extends down the arc tube of the envelope I to a point near the cathode 2 at the opposite end of the device, where each of said wires terminutes in a collector i2. Each cathode lead I of this device is connected to one side of a suit able-"altemating current line of 110 or 220 volts through a ballast resistance l5, this ballast resistance being divided for purposes of symmetry. Each heater inlead G is likewise connected to the opposite side of said line from that to which the associated cathode inlead is connected. The in-' leads III are each connected through a resistance acting cathode.

l6 and a rectifier 34 to the cathode lead 1- which is at the same end of the device, the negative side of said rectifiers being connected to said inleads "I. The resistances IB'rnay be omitted, of course,

' where the rectifiers 34 have sufficient resistance.

The operation of this device is substantially identical, on any given half. cycle, with the operation of the device of Fig. l. The discharge spreads along the wire H to the cathode 2 which at that moment is, serving as an anode in the way which has been described in connection with that figure, establishing the main are which persists for the remainder of that half cycle. When the alternating current potential reverses the discharge spreads in the same manner along the other wire II to the other cathode as an anode, reestablishing the main arc in the opposite direction through the envelope I. Due to the rectifiers 34 the wires II- are in eflect disconnected during the half cycle when each would otherwise be connected to the Thus during that half cycle the wire H is in effect floating in space, and more nearly assumes space potential than would be possible ifit were connected to the. negative side of the line atthat time. The sputtering of particles therefrom by positive ion bombardment is I thereby greatly reduced, although it cannot be entirely obviated as itcan in the circuit of Fig. 2, if a wire having concentrated resistance isused. This device has the compensating advantage.

however, that its auxiliary apparatus is more simple than that used in the circuit of Fig. 2. Moreover, if a wire of uniform resistance is employed, a single wire may obviously be used, opposite ends thereof being connected to each side of the line through a rectifier, in the same fashion as the separate wires of Fig. 3. with this construction all sputtering is avoided, at some sacrifice of the effectiveness of the wire to start the arc.

While I have shown and described my invention by reference to particular structures it is to be understood that it is not limited thereto, but that various changes, substitutions and omissions. within the scope of the appended claims, may be made therein without departing from the spirit thereof.

I claim as my invention:

1. An electric gaseous dischargedevice comprising a sealed envelope containing a gaseous atmo'sphere, a cathode and another main electrode sealed into said envelope, and a resistance wire constituting an auxiliary anode electrically connected to the latter electrode and extending within said envelope from a point near said electrode to a point near said cathode, the resistance of saidwire per unit distance along the arc path between said cathode and the other electrode progressively increasing in the direction of said cathode. v

2. An electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere, a cathode and another electrode sealed into said envelope, and a resistance wire constituting an auxiliary anode electrically connected to the latter electrode and extending within said envelope from a point near said electrode to a point near saidcathode, the effective anodesurface of said wire per unit distance along the arc path between said cathode and the other electrode progressively decreasing in the direction of said cathode.

3. An electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere, a cathode and another main electrode sealed into said envelope, and a resistance wire constituting an auxiliary anode connected to the latter electrode through a resistance and extending within said envelope from'a point near said electrode to a point near said cathode, the resistance of said wire per unit distance along the arc path between said cathode and the other electrode progressively increasing in the direction of said cathode while the effective anode surface thereof per said unit of distance progressively decreases in the direction of said cathode.

4. An electric gaseous discharge device having a sealed tubular envelope containing a gaseous atmosphere, an electrode at each end of said envelope, each of said electrodes being adapted to serve as anode or cathode, .two resistance wires within said envelope, each extending from a point near one of said electrodes to a point near the other thereof, one of said wires being connected to one of said electrodes, while theother wire is connected to the other electrode, the resistance of each of said wires per unit distance along said envelope progressively increasing in a direction away from the electrode to which it is connected.

5. An electric gaseous discharge device having a sealed tubular envelope containinga gaseoul I 2,030,376 atmosphere, an electrode at each end of said envelope, each of said electrodes being adapted to serve as anode or cathode, two resistance wires within said envelope,'each extending from a point near one of said electrodes to a point near the other thereof, one of said wires being connected to one of said electrodes through a rectifier, while the other wire is connected to the other electrode through another rectifier, whereby each of said wlres is energized as an anode whenever the electrode to which it is connected is serving as an anode, the resistance of each of said wires per unit distance along said envelope progressively increasing in a direction away from the electrode to which it is connected.

6. In combination, an electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere, a cathode and two anodes sealed into said envelope, and a resistance wire extending from a point near said cathode to a point near said anodes, means to connect said anodes to a source of alternating current, means to connect said cathode to the midpoint of said source through an inductance, and means to connect said wire to both sides of said source through a rectifier, whereby said wire is always maintained at a positive potential with respect to said cathode. v

7. An electric gaseous discharge device having a sealed tubular envelope containing a gaseous atmosphere, a cathode at one end-or said envelope and two anodes of the opposite end of said envelope, and a resistance wire extending i'rom a point near said anodes to a point near said cathode, said wire being connected to at least one of said anodes through a rectifier.

8. An electric gaseous discharge device having a sealed tubular envelope containing a gaseous atmosphere, a cathode at one end 01 said envelope, two anodes at thevopposite end of said envelope, and a resistance wire extending from a point near said anodes to a point near said cathode, said wire being connected to each- 01' said anodes through a rectifier.

9. An electric gaseous discharge device having a sealed tubular envelope containing a gaseousatmosphere, a cathode at one end of said envelope, two anodes at the opposite end of said envelope, and a resistance wire extending from a point near said cathode to a point near said anodes, said wire being connected to each 'of said anodes through a rectifier, whereby said wire serves as an auxiliary anode, the resistance of said wireper unit length along said envelope progressively increasing in the direction of said cathode.

10. An electric gaseous discharge device having a sealed envelope containing a gaseous atmosphere, a plurality of electrodes sealed into said envelope, two of said electrodes being adapted toserve as anodes, and a resistance wire extending within said envelope, said wire being connected to each of said last mentioned electrodes through a rectifier.

11. The method of starting and operating an electric gaseous discharge device which comprises applying a potential between the electrodes of said device, producing an auxiliary discharge to one of said electrodes, and causing the current fromsaid discharge to produce a steep potential gradient of substantially constant value in that portion of a wire extending toward another electrode which is immediately in advance of said discharge whereby said discharge is caused to travel along said wire to said other electrode.

12. The method of starting and operating an electric gaseous discharge device on an alternatingcurrent source which comprises applying an alternating current potential between the electrodes thereof, and effectively connecting a discharge initiating wire. within said device alternately to opposite terminals of said source, whereby said wire is continuously utilized as an auxiliary anode.

13. The method of starting and operating an electric gaseous discharge device on an alternating current source which comprises applying an alternating current potential between the electrodes thereof, and eflectively connecting a discharge initiating wire within said device to one 01' said electrodes whenever said electrode is positive with respect to the other electrodes, and eitectively disconnecting said wire therefrom whenever said electrode is negative.

CARL E. 

